Detergents today are available in a wide variety of forms such as powders, granules, liquids and gels. Unit dose and concentrated (or compact) detergent forms are becoming increasingly popular due to the convenience they offer the consumer on lower weight and, in the case of unit dose, simplified dosing. The highly concentrated nature of these forms offers further sustainability advantages, such as reduced shipping costs and environmental impact (e.g. carbon footprint).
As detergent compositions age, it is known that they may become more yellow due to any of a number of causes, including, for example, exposure to light, heat, air permeating through the package, natural degradation of the compositions components, or reactions involving formulated components. Further, as many laundry compositions age, their efficacy tends to decline as certain components may degrade with age and lose potency. Consumers accustomed to expiration dates on items understand that formulations have some limited time in which they will function as expected, after which they expect some decrease in the efficacy of the product. However, few if any products provide the consumer a means by which they can assess where a product in their possession is in relation to its expected useful lifespan, even when a date of production is on the package. This date of manufacture cannot provide any information regarding the impact of the conditions to which the product has been exposed between the date of manufacture and the point of purchase. The date of manufacture indicates only the maximum possible freshness and/or functioning of the product at any point in time, but adverse storage conditions lead to deterioration that decreases efficacy of certain ingredients (such as enzymes) and there is no means by which a consumer may estimate the functional age of the formulation.
It is also known that as textile substrates age, their color tends to fade or yellow due to exposure to light, air, soil, and natural degradation of the fibers that comprise the substrates. As such, to visually enhance these textile substrates and counteract the fading and yellowing the use of polymeric colorants for coloring consumer products has become well known in the prior art. For example, it is well known to use whitening agents, either optical brighteners or bluing agents, in textile applications. However, due to the blue or violet hue of traditional bluing agents, formulators have been constrained to using traditional bluing agents in dark blue detergent compositions that show little if any color change over time.
Leuco dyes are also known in the prior art to exhibit a change from a colorless or slightly colored state to a colored state upon exposure to specific chemical or physical triggers. The change in coloration that occurs is typically visually perceptible to the human eye. Most organic compounds have some absorbance in the visible light region (400-750 nm), and thus more or less have some color. As referred to herein, a dye is considered as a “leuco dye” if it did not render a significant color at its application concentration and conditions, but renders a significant color in its triggered form. The color change upon triggering stems from the change of the molar attenuation coefficient (also known as molar extinction coefficient, molar absorption coefficient, and/or molar absorptivity in some literatures) of the leuco dye molecule in the 400-750 nm range, preferably in the 500-650 nm range, and most preferably in the 530-620 nm range. The increase of the molar attenuation coefficient of a leuco dye before and after the triggering should be bigger than 50%, more preferably bigger than 200%, and most preferably bigger than 500%.
As such, there remains a need for a consumer to assess the estimated functional age of a unit dose composition and, thereby, the composition's estimated efficacy.
It has now surprisingly been found that the presently claimed leuco colorants incorporated into the film of a unit dose composition develop their color over time in response to environmental factors such as the temperatures to which they have been exposed, thereby providing the consumer with an estimated functional age of the compositions. Additionally, where the leuco colorants develop blue color, they can be used to counteract the natural yellowing of aged detergent compositions, and will typically be designed to deposit on fabric through the wash, either in their leuco form, or in their oxidized form to provide a whiteness enhancement to aged fabrics.